Move source CSS to src directory so it can be excluded from the zip

.gitignore

@@ -1 +1,2 @@
-node_modules
+node_modules
+.DS_Store

package.json

@@ -5,7 +5,7 @@
   "main": "index.js",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1",
-    "build:css": "postcss assets/css/styles.css > assets/css/styles.min.css"
+    "build:css": "postcss src/styles.css > assets/css/styles.min.css"
   },
   "repository": {
     "type": "git",